Magnet-based sensor devices are frequently used to detect movements and/or positions. In general, for such devices, a magnet arrangement is mounted to a first part of a device, and a magnetic field sensor arrangement is mounted to a second part of the device, the first part being moveable with respect to the second part. When the first part moves relative to the second part, the magnetic field sensed by the sensor arrangement changes, thus enabling a detection of movement and/or position.
One type of such sensors are angular magnetic sensors, which sense for example an angular position or a rotational speed. In such devices, for example a magnet arrangement may be mounted to a rotating shaft, and a sensor arrangement which is stationary with respect to the rotating shaft senses changes of the magnetic field when the shaft rotates. Such devices may e.g. be used in the automotive field to determine angular position and/or rotational speed of various components of an automobile.
One type of such sensors uses magnetoresistive sensor elements, which respond to a magnetic field components in a plane perpendicular to the rotation axis of the shaft. Several types of magnetoresistive sensor elements are known, which may be based on anisotropic magnetoresistive effect (AMR), giant magnetoresistive effect (GMR), colossal magnetoresistive effect (CMR) or tunneling magnetoresistive effect (TMR). Instead of magnetoresistive sensor elements in some cases also vertical Hall devices may be used which also detect magnetic field components perpendicular to the rotation axis. Such sensor devices have the disadvantages that they are quite sensitive to magnetic disturbances (e.g. stray fields). Their advantage is that they are comparatively insensitive to manufacturing tolerances, in particular tolerances as regards the positioning of various components.
This type of magnetic sensor device may be referred to as perpendicular magnetic angle sensor herein.
Another type of angular magnetic sensor devices uses a couple of Hall plates (e.g. at least three) arranged on a plane perpendicular to the rotation axis of a shaft to which a magnet arrangement is mounted. Such Hall plates are for example positioned around a center where the rotation axis intersects the plane on which the Hall plates are arranged. The Hall plates generally are sensitive to a magnetic field in a direction parallel to the rotation axis. When the magnet rotates, the signals of the different Hall plates are e.g. combined in such a way to extract the slope of the vertical magnetic field component parallel to the direction of the rotation axis in one or more, preferably at least, orthogonal directions. These devices therefore operate as vector gradiometers, detecting gradients of the magnetic field in two directions. This type of magnetic sensor device may be referred to as axial magnetic angle sensor herein, because they primarily detect axial magnetic field components.
Such axial magnetic angle sensors are generally more robust against magnetic disturbances as the previously explained perpendicular magnetic angle sensors. On the other hand, they tend to be sensitive to small assembly tolerances of the device, such that for example a slight lateral misalignment between magnetic arrangement and sensor arrangement may cause comparatively large errors in measured angles.
While some optimized magnet arrangement to reduce sensitivity to assembly tolerances had been discussed previously in the art, conventional solutions for optimized magnets may have drawbacks like small magnetic fields, which reduce the sensed signal.
It is therefore an object to provide possibilities to provide improved magnet arrangements and magnetic angle sensor devices, in particular devices which are less susceptible to assembly tolerances and still apply large magnetic fields on the sensor elements.